1. Field of the Invention
The invention relates to transformers. More particularly, the invention relates to noise-limiting transformers suitable for use in, e.g., bidirectional communications schemes using local access coaxial cables.
2. Description of the Related Art
Most homes in the United States have coaxial cable lines installed to their homes, primarily for entertainment purpose. The use of the coaxial cable lines for two-way communications, either entirely or locally as a part of a Hybrid-Fiber-Coax (HFC) communications system arrangement with the coaxial cable portion connecting the distribution fiber node to each home, is an economically viable alternative to the use of existing telephone lines (i.e., conventional twisted pair copper wires), or yet-to-be realized fiber-to-home or wireless local access configurations.
Currently, the HFC architecture is used mostly for one-way (downstream) transport of multiplexed signals to subscribers, e.g., with a downstream bandwidth of about 50-750 Megahertz (MHz). However, the HFC architecture is being considered as a promising, bidirectional, broadband communications infrastructure for the multibillion dollar communications market in part because of the low deployment cost expected. Conventional system architecture uses an upstream bandwidth of about 5-40 MHz, but the possibility of higher frequency (e.g., 750-1000 MHz) regimes also exist as information transmission increases in the future with the addition of more video, Internet and other applications. Accordingly, there exists a need for improved devices and equipment to support and maintain reliable, bidirectional HFC communications systems using this high rate of information transmission.
However, one of the main barriers to the reliable operation of bidirectional HFC communications systems is the noise problem, commonly know as the "ingress". Because the HFC architecture typically consists of conventional tree-and-branch arrangements, the upstream transmission from various subscribers to the headend (central) office is shared. Thus, ingress noise, e.g., from individual subscriber homes and the overall cable structure, are added onto the main upstream transmission signals, inadvertently affecting the transmission of other subscribers. Such behavior typically is referred to as noise funneling. See, e.g., C. A. Eldering, e.g., "CATV Return Path Characterization for Reliable Communications", IEEE Communications Magazine, August 1995, p. 62.
Accordingly, a need exists for noise-limiting devices to reduce the problem of ingress noise and thereby improve efficiency among two-way communications using, e.g., HFC architecture.